The use of certain alkyl methacrylate polymers as electron beam degradable polymers for the formation of resist masks which are useful in the fabrication of integrated circuits, printing plates and the like has been proposed heretofore. For instance, U.S. Pat. No. 3,535,137 granted on Oct. 20, 1970 to Haller et al. teaches among other things the use of methacrylate polymers containing a quaternary carbon in the polymer backbone such as polymethyl methacrylate, and copolymers of methyl methacrylate with 2-hydroxy ethyl methacrylate, for such purpose. In addition, U.S. Pat. No. 3,779,806 granted on Dec. 19, 1973 to Gipstein et al. discloses the use of certain polymers of t-butyl methacrylate for such purpose. Related discussions are contained in the articles "Polymethyl Methacrylate as an Electron Sensitive Resist" by R. A. Harris, J. Electrochemical Society, Vol, 120, No. 2, pp. 270-274, Feb. 1973, and "A Modified Methacrylate Positive Electron Resist" by E. D. Roberts, Applied Polymer Symposium No. 23, pp. 87-98 (1974).
Generally the resist masks are prepared by coating a film on layer of the polymeric material on a substrate, and then exposing portions of the film or layer to an electron beam in a predetermined pattern of the desired mask with sufficient exposure to degrade the polymeric material in the exposed areas. Next, the electron beam degraded polymeric material is removed from the exposed area with a solvent which has a marked differential solubility for the degraded products and for the unexposed polymeric material.
In the manufacturing of such devices as integrated circuits by electron beam lithography, it is important that the energy dosage and exposure time required to sufficiently degrade the exposed pattern of the polymeric material for high resolution be as low as possible to provide a process which is both practical and economical to carry out.
Accordingly, it is an object of the present invention to provide a process for forming a positive resist image by exposure to electron beams wherein the polymeric material employed has improved resist sensitivity and resolution.
Another object of the present invention is to provide a process for the formation of high resolution polymeric positive resists utilizing an electron beam activated polymer of certain polymeric materials containing alkyl methacrylate units, which polymer exhibits excellent film-forming characteristics, differential solubility in solvents between exposed and unexposed areas, resistance to various etch solutions, and ready removal of unexposed portions with simple solvents.
The use of polymethyl methacrylate suggested heretofore has apparently been limited to techniques in semiconductor processing which employs temperature not exceeding about 135.degree. C (see M. Hatzakis, Journal Electrochemical Society, 116, 1033, 1969). Accordingly, it is an object of the present invention to provide a process wherein at least some of the polymeric materials employed has increased thermostability as compared to polymethyl methacrylate homopolymers. The present invention makes it possible in certain instances to provide semiconductor processing such as sputter etching, ion-beam etching, ion-beam doping, or lift off metallurgy techniques wherein the polymeric material can be subjected to relatively high temperatures (i.e., above about 135.degree. C).